Structural Invariance of Sunspot Umbrae Over the Solar Cycle: 1993-2004

Understand

Measurements of maximum magnetic flux, minimum intensity, and size are presented for 12 967 sunspot umbrae detected on the NASA/NSO spectromagnetograms between 1993 and 2004 to study umbral structure and strength during the solar cycle.

• The umbrae are selected using an automated thresholding technique.
• Measured umbral intensities are first corrected for a confirming observation of umbral limb-darkening.
• Log-normal fits to the observed size distribution confirm that the size spectrum shape does not vary with time.